C # version multiselected DataGrid

Datagrid|select using System;
Using System.Drawing;
Using System.Collections;
Using System.Windows.Forms;
Namespace Csharpdatagrid
{

public class MyDataGrid:System.Windows.Forms.DataGrid
{
Private ArrayList m=new ArrayList ();
Array Multiselectedindex
{
Get
{
Return This.m.toarray (typeof (int));
}
}

protected override void OnMouseDown (System.Windows.Forms.MouseEventArgs e)
{
Console.WriteLine ("Datagrid has hit");
Point _POSDG = new Point (E.X,E.Y);
System.Windows.Forms.DataGrid.HitTestInfo _HITDG =base. HitTest (_POSDG);
if (Hitdatagrid (_HITDG))
{
Base. OnMouseDown (e);
}
Base. OnMouseDown (e);
}
private bool Hitdatagrid (Datagrid.hittestinfo Hit)
{
Try
{
Switch (Mydatagrid.modifierkeys)
{
Case Keys.control:
if (hit.row>-1)
{
if (M.indexof (hit.row) >-1)
{
M.remove (Hit.row);
This. Unselect (Hit.row);
}
Else
{
M.add (Hit.row);
This. Select (Hit.row);
}
}
return false;
Case Keys.shift:
if (hit.row>-1)
{
foreach (int intindex in M)
{
This. Unselect (Intindex);
}
M.clear ();
int _count;
int _intstep;
if (hit.row>this. Currentrowindex)
{
_intstep=1;
}
Else
{
_intstep=-1;
}
For (_count=this. Currentrowindex; _count==hit.row;_count+=_intstep)
{
M.add (_count);
This. Select (_count);
}
}
return false;
Default
foreach (int _intindex in M)
{
This. Unselect (_intindex);
}
M.clear ();
if (Hit.type==datagrid.hittesttype.rowheader)
{
M.add (Hit.row);
}
return true;
}
}
catch (System.Exception ex)
{
Throw ex;
}
}
}
}